(i) Field of the Invention
This invention relates to chemical vapour deposition, and more particularly to semiconductor film deposition by chemical vapour deposition.
More specifically, the invention concerns an apparatus and a method for producing a semiconductor device having a PIN junction, depositing semiconductor films by plasma chemical vapour deposition (hereinafter referred to simply as "PCVD" for brevity) employing a single reaction chamber or a series of reaction chambers (a multi-chamber system) for laminating a P-type non-single crystal semiconductor film, an I-type non-single crystal semiconductor film and an N-type non-single crystal semiconductor film successively on a substrate in the respective reaction chambers.
(ii) Description of the Prior Art
In a conventional CVD apparatus, for instance, in a PCVD apparatus where the pressure of the reaction system is as high as 0.01 to 10 Torr, it has been the general practice to employ an exhaust system with a rotary pump alone due to a difficulty of providing a turbo pump for the purpose of producing a higher degree of vacuum. However, since a rotary pump which is solely resorted to by the exhaust system of the conventional PCVD apparatus involves discontinuous rotational movements, there occur reverse flows of the atmospheric air (especially oxygen) from the exhaust system which is in contact with the atmosphere, the backflow air partly entrained in oil and creeping into the reactor by regasification, as a result infusing into the film being formed in the reactor. Therefore, the oxygen concentration in the film sometimes reaches to a value of 5.times.10.sup.19 to 2.times.10.sup.20 cm.sup.-3 in the case of a silicon film.